1. Field of the Invention
The present invention relates to a natural convection-driven polymerase chain reaction (PCR) apparatus and method using a disposable polymer chip; and, more particularly, to a natural convection-driven PCR apparatus and method, which can periodically change the temperature of a sample to make a natural convection-driven flow in a loop-shaped channel by forming the loop-shaped channel on a disposable polymer chip and contacting heating metal members maintained at different temperatures with channels.
2. Description of Related Art
Generally, biochip, biosensor, and chemical sensor for biochemical analysis are required to make a reaction by applying a temperature change to a sample. For the temperature charge, a variety of heating methods have been proposed. A typical device for making a reaction by applying a temperature change to a sample is a deoxyribonucleic acid (DNA) amplification device that amplifies DNA by adding an enzyme to a DNA template and applying a predetermined temperature cycling.
More specifically, the temperature cycling is to change a temperature to two or three different degrees. That is, the temperature cycling changes a temperature to different degrees in order for a denaturation step for separating a DNA double helix, an annealing step for controlling the DNA template to find a complementary pair, and an extension step for growing the DNA. The DNA amplification due to the temperature change is referred to as a polymer chain reaction (PCR).
The heating methods for changing the PCR temperature may be classified into two categories. The first method is to change a temperature of a sample by externally applying a temperature change to a sample filled and stopped in a chamber. The second method is to change a temperature of a sample by moving the sample to an environment having a desired temperature condition. The first method does not require an additional fluid control because the sample is stopped. However, a lot of time is taken to change the external temperature environment when a thermal capacity of the external environment is large. In addition, a control operation for the temperature change is additionally required. Thus, the first method becomes complicated.
The second method can rapidly and accurately change the temperature of the sample because the external temperature environment can be constantly monitored. However, the second method requires a fluid control operation for moving the sample.
To overcome the disadvantages of the two methods, a method for periodically applying a temperature change to a sample has been proposed. This method uses a natural convection to rapidly and accurately change the temperature of the sample by passing the sample through a constant temperature zone, without additional external fluid control operation.
The natural convection is a flow phenomenon derived from the generation of a buoyant force when the density of a fluid placed under a gravitational field is changed due to heat. The fluid flows downward in a relatively cold external environment and flows upward in a relative hot external environment. In the PCR, although there is a difference according to kinds of the DNA sample, which is an amplification target, the denaturation step is performed in a temperature range from 90° C. to 97° C., the annealing step is performed in a temperature range from 50° C. to 65° C., and the extension step is performed in a temperature range from 68° C. to 74° C. Using the temperature difference, the natural convection flow may be generated.
Since this flow is naturally generated at any place where the gravitational field exists, the external fluid control operation for moving the sample may be omitted. The known PCR apparatus and method using the natural convection will be described below.
Examples of the PCR using the natural convection are disclosed in U.S. Pat. No. 6,586,233, entitled “Convectively Driven PCR Thermal-Cycling”, U.S. Patent Application Publication No. 2004/0152122, entitled “Method And Apparatus for Amplification of Nucleic Acid Sequences by Using Thermal Convection”, and U.S. Patent Application Publication No. 2006/0216725, entitled “Polymer Chain Reaction Apparatus Using Marangoni Convection And Polymer Chain Reaction Method Using The Same.” In U.S. Pat. No. 6,586,233, trenches for thermal isolation are installed and a pouch for containing a sample is inserted into a heating block heated to two different temperatures. The PCR temperature cycling is achieved using the convection generated when the sample is clamped.
In U.S. Patent Application Publication No. 2004/0152122, a relatively high temperature region is located lower in height than a relatively low temperature region, thereby forming a spatial temperature distribution. The convection is generated by spatially changing a temperature of a sample using the spatial temperature distribution. In U.S. Patent Application Publication No. 2006/0216725, both sidewalls of a chamber are maintained at a constant temperature and Marangoni convection is used. The Marangoni convection is generated by a surface tension gradient resulting from a temperature difference in an interface between a sample and air.
A paper entitled “Thermosiphon-Based PCR Reactor: Experiment and Modeling”, Analytical Chemistry, Vol. 76, No. 13, Jul. 1, 2004, discloses a PCR method that constantly maintains temperatures of three aluminum heating blocks and forms a loop using a tube.
The conventional PCR apparatuses and methods disclosed in the above-described documents and paper uses the pouch-shaped sample container or tube, have the spatial temperature distribution, and generate the natural convection by applying the temperature change. In the case of using the pouch or tube, there is an inconvenience in placing the sample and the tube must be replaced when it is reused. Thus, mass-production is difficult. In addition, the conventional PCR apparatus has difficulty in effectively eliminating thermal interference using the spatial temperature change. Further, temperature interference may occur because the sidewall of the sample is locally heated and the sample does not change to a desired temperature in each temperature zone.